Question

Write the molecular formula of sodium chloride.

Answer 1

Molecular formula: molecular formula of a compound is the symbolic representation of the one molecule of a compound which shows the number of atom of each element that is present in it.

For example, ${\mathrm{H}}_2\mathrm{O}$(water) molecule represents that water is made up of 2 atoms of hydrogen element and one atom of oxygen.

Steps for writing molecular formula:

• First write symbols of elements present in that compound. Elements with positive valency (metals) are placed on the right-hand side followed by the elements with the negative valency(non-metals).
• Now write the valency of each element below it.
• Now interchange the valency by the criss-cross method.
• The interchange valency is placed as a subscript of each element.
• If the compound is formed of polyatomic ions( ${\mathrm{SO}}_4^{2-}$)then the number of ions present in that compound is represented by enclosing the formula of the ion in a bracket and writing its number outside the bracket. For example, $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$(calcium hydroxide)

Sodium chloride

• First, write symbols and valency of sodium (positive ion toward the right) and chloride (negative ion towards the left).

$\mathrm{Na}$ (sodium) $\mathrm{Cl}$ (chloride)

(+1) (-1)

• Now interchange the valency by the criss-cross method and write interchange valency at the base of each ion.
• Thus the formula becomes$\mathrm{NaCl}$.